The present invention relates to the field of sensors and, more particularly to the fields of sensors and methods of mounting sensors.
Over the years sensors have been developed which include transducers that possess a specific preferred orientation in relation to an electrical field, a magnetic field, or a mechanical force to be sensed. To maximize the response of the sensor, the transducer must be oriented in the direction of this field or force. Some examples of electrical or magnetic field sensors are position and proximity sensors such as Hall effect, magnetoresistor, capacitive, and inductive sensors and electrical current field sensors. Mechanical force sensors generally measure the flow or pressure of a liquid or gas, the mechanical stress or weight of an object, or the acceleration of an object. These sensors generally have a preferred orientation of the transducer to the electrical or magnetic field or to the physical force being sensed in order to maximize the sensitivity of the transducer.
Also, there may be other extraneous electrical or magnetic fields or mechanical forces in the system. The transducer may have to be oriented relative to these extraneous fields or forces in a specific direction to reduce the sensitivity of the transducer to them. This helps to eliminate sensing errors or noise caused by the movement of other objects or caused by the presence of other fields or forces.
These sensors also conventionally employ signal conditioning circuitry or a signal conditioner to amplify or otherwise condition the transducer signal. The signal conditioner is needed, for example, because the transducer signal is usually too low in magnitude to overcome noise or contains a large offset or other error signals that overdrive sensitive monitoring equipment. Otherwise, the transducer signal is not conducive to transmission over a distance to a remotely located sensor monitoring circuit.
Additionally, the sensors are often used in mechanical systems that have restrictions on overall size, weight, structural integrity, reliability, and cost. For these reasons, the sensor is usually made as small as possible by using transducers and signal conditioners that are electronic or that contain electrical devices manufactured on semiconductor wafers.
A first significant problem with transducers and signal conditioners which are manufactured as semiconductor devices, however, is that the electrical conductivity or other operating characteristics change significantly in response to changes in temperature. This can result in a significant change in transducer output as a function of temperature. Because most of the mechanical systems in which these sensors operate can experience rather significant changes in operating temperature, the effects of these temperature changes on the sensor output constitutes an error signal and should therefore be eliminated or reduced if possible.
The elimination of this error signal is usually a function of the signal conditioner and is usually accomplished in several related ways. The transducer and signal conditioner that are to be used together in any single sensor are usually manufactured at the same time using the same manufacturing process and are located as closely as possible in relation to each other on the same semiconductor wafer. This is done primarily to make the physical proportions of the components that comprise the transducer and the signal conditioner equal or proportional in width, length, and depth of features and to have equal relative concentrations of the various semiconductor materials used to form the components. For instance, all transistor bases, emitters, and collectors will be essentially the same relative size even if they are manufactured slightly larger or smaller than intended, and will have generally the same concentrations of materials regardless of whether they are at the intended levels of these various concentrations. The electrical conductivity of any particular electrical component in the transducer or the signal conditioner is proportional to the size of its features as well as the concentration of materials from which the component is manufactured. Any two components on the wafer located in close proximity to each other with the same dimensions and formed from the same relative concentrations of materials generally will have equal electrical conductivities if they are at the same temperature. Also, any component located near another component which has the same concentrations of materials but whose dimensions are not equal but are proportional to the other component will have an electrical conductivity that is proportional in the same degree as the dimensions if they are both at the same temperature. Because the size and composition of these components are set during manufacture, any short term changes in their electrical conductivity under identical electrical conditions are generally caused only by changes in the temperature of the component.
In this manner any specific component or collection of components on the transducer required for proper operation can be duplicated in the signal conditioner at the same size or at a specific proportional scale and with equal concentrations of materials. For example, some transducers employ four resistors in a Wheatstone bridge configuration. Any one or more of these resistors can be made with equal dimensions and with equal composition of materials on the signal conditioner. Under these conditions, the electrical conductivity of both pairs of resistors generally will be equal if their temperatures are equal. In any case, if the temperature of the transducer components is the same as the temperature of the signal conditioner components, both the transducer and signal conditioner will contain components that experience equal or proportional electrical conductivity due to the effects of temperature alone.
One of two methods are generally used in association with a signal conditioner to determine this change in electrical conductivity and then to produce a corresponding signal that cancels the effects of this change on the transducer output. First, if size allows, a complete duplicate of the transducer can be made on the signal conditioner. This duplicate transducer is then electrically, magnetically, or physically shielded from the field or force being sensed or is in some manner made unresponsive to the sensed parameter. An equal excitation or drive signal is then applied to both the components comprising the active transducer and the components comprising the duplicate passive transducer on the signal conditioner. The output of the signal conditioner passive transducer is then relative only to temperature and is then subtracted from the output of the active transducer that responds to the field or force. This is usually accomplished in a differential amplifier or a similar electronic circuit.
A second method, for example, can be used where space for the signal conditioner is more limited. A representative part of the transducer at any proportion can be duplicated on the signal conditioner. This representative part can be chosen to be a part that is unresponsive to the parameter being sensed or can be physically oriented to a position where it is not affected or otherwise shielded from the parameter being sensed. In any case, it is designed so its electrical conductivity is proportional only to changes in temperature. The change of the transducer output due to the cumulative changes of electrical conductivity of all transducer components due only to changes in temperature is determined by direct measure or by mathematical calculation during the sensor design phase. This yields a specific level of transducer output change per degree of change in temperature. This information is used to design a circuit with a specific amount of gain determined by the relationship of the change in electrical conductivity of the signal conditioner duplicate component to the change in transducer output caused by a change in temperature. This circuit monitors the change in electrical conductivity of the signal conditioner duplicate component and then amplifies this change by the amount required to yield an equivalent signal level change that is then subtracted from the transducer output as above.
Long term changes of electrical conductivity are a second significant problem in semiconductor components. This is usually caused by electromigration of the atoms of the material comprising the components from their positions as manufactured along paths of electrical current into areas that are not designed to contain them. For instance, the atoms comprising the base structure of a transistor can migrate into the areas occupied by the emitter and the collector, and vice versa. This changes both the physical size of the component as well as its concentration of the materials comprising the component. Any component in the transducer will experience these effects the same as an identical component in the signal conditioner provided the current through both components is kept equal over the life of the sensor. This is felt the same way as the short term effects of temperature as above by both components in the transducer and in the signal conditioner and is thus effectively compensated for in the same manner as short term changes in temperature.
During the manufacturing process, both the transducer and the signal conditioner are formed on a common surface on the wafer known as the planar surface. Since components are not usually formed on top of other components, this results in transducers and signal conditioners that have a large surface area relative to the depth of the devices. The area taken up by these devices is generally measured along this planar surface. The depth of all such semiconductor devices is usually fixed by design considerations and is not relative to the number of devices.
Prior art sensors generally manufacture the signal conditioner and transducer on the same wafer and interconnect the two using conductive traces defined directly on the wafer. The prior art sensors are then installed as a single monolithic chip in the sensor. Since the transducer generally should be oriented in a specific direction relative to the field being sensed, this requires that the signal conditioner be oriented also to the field in like manner.
Also, the amount of area occupied by the transducer is much smaller than the area occupied by the signal conditioner. Orientation of both a transducer and a signal conditioner along the same plane generally produces a larger cross section for the sensor than could be achieved by orienting the transducer to the field and orienting the signal conditioner separately in whatever direction needed to realize the smallest cross section. Because the signal conditioner does not require a specific orientation in relation to the field, a much smaller cross section in relation to a specific direction of measurement can be realized by changing the orientation of the transducer and signal conditioner so they are orthogonal. This can only be accomplished if the transducer and signal conditioner are physically separated and electrically connected using some means other than the conductive traces so the transducer can be oriented to the field or force separately from the signal conditioner.
With the foregoing in mind, the present invention advantageously provides a compact sensing apparatus that achieves a smallest cross section in relation to a defined axis. The present invention also advantageously provides a compact sensing apparatus and method which simplify manufacture of a sensing apparatus or sensor by providing means for orienting the transducer in a selected direction in relation to the signal conditioner.
The present invention accomplishes these objects and advantages relating to field orientation by positioning a transducer in a specific orientation relative to a signal conditioner in a sensing apparatus. The transducer and signal conditioner can be manufactured simultaneously on a semiconductor wafer and means are employed to either leave the transducer and signal conditioner oriented as manufactured or to arrange them physically at right angles to each other to provide the maximum sensitivity to the field for the transducer and the minimum cross section for the sensing apparatus along its axis of orientation.
The present invention also accomplishes the objects and advantages of the orientation of the transducer and signal conditioner by employing electrically conductive pins that are rigid. The pins provide electrical connection between the transducer and the signal conditioner and between the signal conditioner and external sensor monitoring equipment.
More particularly, a compact sensing apparatus according to the present invention preferably includes plurality of mounting pins. Each of the plurality of mounting pins preferably includes a first pin portion and a second pin portion connected to the first pin portion at a predetermined angle. The first pin portion preferably has a length less than the second pin portion, and the predetermined angle is preferably less than 180 degrees and more preferably in the range of about 70-110 degrees. A transducer is formed from a semiconductor wafer mounted to the first pin portion for generating a transducer signal. Signal conditioning means also is formed from the same semiconductor wafer and mounted to the second pin portion for conditioning the transducer signal.
A compact sensing apparatus according to another aspect of the present invention preferably includes a plurality of mounting pins. Each of the plurality of mounting pins includes a first pin portion and a second pin portion connected to the first pin portion at a predetermined angle. The first pin portion preferably has a length less than the second pin portion. A transducer is mounted to the first pin portion for generating a transducer signal. A signal conditioner is mounted to the second pin portion for conditioning the transducer signal. The signal conditioner is preferably mounted to the second pin portion so that the lateral extent of the signal conditioner is generally perpendicular to the lateral extent of the transducer.
According to other aspects of the present invention, a compact sensing apparatus has the plurality of mounting pins which are defined by a plurality of spaced-apart and elongate mounting pins. The lengthwise extent of each of the plurality of spaced-apart and elongate mounting pins is spaced-apart from and generally parallel to the lengthwise extent of another one of the plurality of pins. The plurality of spaced-apart and elongate mounting pins include a plurality of generally coaxially aligned and laterally spaced-apart mounting pins. Each of the laterally spaced-apart portions extending between the generally coaxially aligned mounting pins is positioned at a different lengthwise extending location than another generally parallel and spaced apart plurality of elongate mounting pins so that at least two of the laterally spaced-apart portions define a plurality of staggered gaps extending between the generally coaxially aligned mounting pins. The plurality of staggered gaps thereby advantageously form electrical isolation between the plurality of generally coaxially aligned mounting pins and thereby increase the stiffness of the sensing apparatus. The plurality of mounting pins are each formed of an electrically conductive rigid material and positioned so as to define electrical connectors for the transducer and the signal conditioning means and to provide physical support for the transducer and the signal conditioning means mounted thereto.
Additionally, each of the transducer and the signal conditioning means are preferably formed on the same surface, e.g., the upper surface, of the same semiconductor wafer substrate. A plurality of bonding pads are also formed on the upper surface of the same semiconductor wafer substrate for bonding the transducer and the signal conditioning means to the plurality of mounting pins. Also, a plurality of conductive traces are preferably formed in the same substrate to provide conductive paths between the transducer and the signal conditioning means. The transducer can include a planar surface for more sensitively sensing a field having flux lines extending either generally perpendicular to the planar surface or generally parallel to the planar surface.
According to still another aspect of the present invention, the first and second pin portions of each of the plurality of mounting pins of the compact sensing apparatus preferably is a single unitary pin. The single unitary pin preferably includes a bend formed therein having an angle of bend defining the predetermined angle of orientation of the first and second pin portions. The transducer can also include a channel formed closely adjacent an edge thereof for adaptively positioning the transducer closely adjacent the bend so that the transducer adaptively clears the bend of each of the plurality of mounting pins. The transducer advantageously can be connected to either a forwardly extending surface of the first pin portion which extends away from the signal conditioning means or to a rearwardly extending surface of the first pin portion which extends toward said signal conditioning means or to either of two surfaces on the second pin portion.
The present invention also includes methods of compactly mounting a sensing apparatus. The method preferably includes the steps of forming a transducer and a signal conditioner from the same semiconductor wafer and providing at least two mounting surfaces. The at least two mounting surfaces are oriented with respect to each other at a predetermined angle. The predetermined angle is preferably less than 180 degrees and more preferably is in the range of about 70-110 degrees. The method also includes connecting the transducer to one of the at least two mounting surfaces and connecting the signal conditioner to another one of the at least two mounting surfaces.
Another method of compactly mounting a sensing apparatus according to the present invention preferably includes providing a transducer and a signal conditioner and positioning the signal conditioner so that the lateral extent thereof is generally perpendicular to the lateral extent of the transducer. The transducer and the signal conditioner are each respectively mounted on at least two mounting surfaces. The at least two mounting surfaces are preferably oriented with respect to each other at a predetermined angle.